Question

Chứng minh rằng:  1/21+ 1/22 + 1/23 +...+ 1/50< 1+1/2                          

Answer 1

khoq thế

Answer 2

Lê Văn Đức loại như mày chỉ copy bài là giỏi thoy

Answer 3

ta có 1/21+1/22+1/23+.....+1/50=(1/21+1/22+....+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)

ta có 1/21<1/22<1/23<...<1/30=>(1/21+1/22+...+1/30)<10x1/21=10/21<10/20=1/2

tương tự =>(1/31+...+1/40)<1/3<1/2;(1/41+...+1/50)<1/4<1/2

=>nó <3.1/2=3/2=1+1/2(đpcm)

Answer 4

Ta có: 1/21 + 1/22 + 1/23 + ... + 1/50

Ta có; 1/20 + 1/20 + 1/20 < 

Answer 5

dùng phương pháp trội nhóm

Answer 6

ta có 1/21+1/22+1/23+.....+1/50=(1/21+1/22+....+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)

ta có 1/21<1/22<1/23<...<1/30=>(1/21+1/22+...+1/30)<10x1/21=10/21<10/20=1/2

tương tự =>(1/31+...+1/40)<1/3<1/2;(1/41+...+1/50)<1/4<1/2

=>nó <3.1/2=3/2=1+1/2(đpcm)

Ai k mk mk k lại!

Answer 7

ta có 1/21+1/22+1/23+.....+1/50=(1/21+1/22+....+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)

ta có 1/21<1/22<1/23<...<1/30=>(1/21+1/22+...+1/30)<10x1/21=10/21<10/20=1/2

tương tự =>(1/31+...+1/40)<1/3<1/2;(1/41+...+1/50)<1/4<1/2

=>nó <3.1/2=3/2=1+1/2(đpcm)

Ai k mk mk k lại!

Answer 8

ta có 1/21+1/22+1/23+.....+1/50=(1/21+1/22+....+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)

ta có 1/21<1/22<1/23<...<1/30=>(1/21+1/22+...+1/30)<10x1/21=10/21<10/20=1/2

tương tự =>(1/31+...+1/40)<1/3<1/2;(1/41+...+1/50)<1/4<1/2

=>nó <3.1/2=3/2=1+1/2(đpcm)

Ai k mk mk k lại!

Answer 9

Ta có: 1/21+1/22+1/23+...+1/50

        =(1/21+1/22+1/23+...+1/40)+(1/41+...+1/50)<

          (1/20+1/20+1/20+...+1/20)+(1/20+...+1/20)=1+1/2

suy ra: 1/21+1/22+1/23+...+1/50<1+1/2

Answer 10

Ta có 1/21+1/22+1/23+.....+1/50=(1/21+1/22+....+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)

T a có 1/21<1/22<1/23<...<1/30=>(1/21+1/22+...+1/30)<10x1/21=10/21<10/20=1/2

Tương tự =>(1/31+...+1/40)<1/3<1/2;(1/41+...+1/50)<1/4<1/2

=>Nó <3.1/2=3/2=1+1/2(đpcm)

Answer 11

Tự tính đi zế ợt